The present invention relates to an air dryer assembly for use in a compressed air system for heavy vehicles, locomotives and/or auxiliary devices that use compressed air. Typical heavy vehicle compressed air systems include a compressor for compressing the air, an air dryer assembly for removing moisture and contaminants from the compressed air, a reservoir for storing the compressed air and valves and other pneumatic system components for distributing the compressed air. The present invention finds particular application in conjunction with heavy vehicles that use compressed air to selectively control application of vehicle brakes and will be described with particular reference thereto.
The compressor provides compressed air to a reservoir, the compressed air being used to operate vehicle brakes and other air operated systems associated with the vehicle. Ambient air is typically drawn into a compressor inlet for compression during an air delivery, or charging, cycle. The air brake compressor is typically supplied with oil in order to lubricate bearings and other components of the compressor.
Typically, the air dryer assembly is installed downstream from the compressor for reducing the moisture content of the compressed air. The air dryer assembly delivers substantially dry compressed air to a reservoir for use by braking system components, thereby increasing the service life of braking system components such as valves and pneumatic brake actuators. Providing clean dry compressed air to brake system components reduces maintenance costs. In some air dryers, a desiccant is used to adsorb water vapor as the compressed air passes through the air dryer assembly during a charging cycle. Liquid water and water vapor is adsorbed onto the desiccant. After a period of charging during normal operation, the desiccant becomes entrained with water and requires regeneration (i.e. removal of the water). The desiccant is regenerated through a purge cycle, which comprises passing pressurized air in a reverse direction through the desiccant.
In some air dryer systems, a purge cycle is initiated in response to the reservoir reaching a predetermined pressure and the compressor being in an unloaded state, or not delivering air. The purge cycle continues until all of the air in a purge reservoir is exhausted through the air dryer desiccant. Generally fir a given air vehicle dryer system the purge cycle is the same duration no matter how long the system may have been charging or how entrained with water, or moist, the air dryer desiccant may have been. That is, the duration is the time it takes to empty the purge reservoir. A subsequent purge cycle only occurs after the compressor returns to a delivery cycle, then unloaded again when the reservoir reaches the predetermined pressure. The typical air dryer using a standard purge may not be able to remove all of the moisture in the dryer desiccant, thereby deleteriously passing moisture downstream. The moist air will enter the purge reservoir, so moisture accumulates and subsequent purges would be less effective since moist air is used in the purge.
For the foregoing reasons, there is a need for a new and improved apparatus and methods which address the above-referenced problems.